A HISTORY OF BEDFORDSHIRE England owing to the absence of the latest Cretaceous and earliest Eocene strata. There are great contrasts between the Upper Chalk and the Read- ing Beds, which, when present in this area, lie in contact with it. Palaeontologically the contrast is between the fauna of a deep sea and that of an estuary ; stratigraphically between a nearly pure limestone of organic origin slowly and evenly deposited, and bright-coloured clays, sands, and pebbles accumulated rapidly and distributed irregularly. The arm of the sea in which these beds were deposited extended from the district which is now the south midlands, to Hampshire or beyond, in- cluding the areas known as the London and Hampshire Tertiary Basins. The northern margin of the London Basin runs through the south or Hertfordshire, and beyond and not far from it there is a series of Eocene outliers of considerable extent followed by another of much smaller ones ; and far away to the north, in South Beds, a few very small ones have escaped the complete denudation which has removed the inter- vening mass, testifying to its former extension. These are in the parishes of Caddington, Kensworth, and Studham, the largest being near Ringsall. In the superficial deposits of the valley of the Lea, within our county, there are frequently found large masses of conglomerate or ' pud- ding stone,' which are probably of the same origin as the Hertfordshire conglomerate. As they are but slightly waterworn they may have been dropped into their present position owing to the dissolution of the softer strata of the Reading Beds of which they formed a part. One that was met with in a shallow excavation just south of Luton measured 6 feet long, 3 feet wide, and 2 feet thick. The pebbles of the Reading Beds, which are thus locally consolidated into a conglomerate with a siliceous matrix, are almost invariably chalk-flints, indicating that the higher Cretaceous strata were subjected to an enormous amount of erosion at the beginning of the Eocene epoch. PLEISTOCENE The greatest change of climate which is definitely known to have taken place in this area and western Europe generally, occurred between the Eocene and Pleistocene epochs, tropical conditions giving place to arctic. The tropical fauna and flora of the London Clay became sub- tropical in later Eocene times, and continued so during the Oligocene and Miocene periods. Early in the Pliocene period temperate conditions set in, and before its close the climate had become boreal or arctic. This change or climate was accompanied by considerable alterations in the distribution of land and sea, the whole of south-eastern England from the Severn to the Humber being at first submerged, then rising so far above the waters that Britain became joined to the continent, neither German Ocean nor English Channel existing, and finally again becoming submerged. It was probably about this time, that is towards the close of the Pliocene period and before the last great submergence, that our 24
